Polymer cover induced self-excited vibrations of nipped rolls

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Plant microbiota : implications for human health

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Parviälyyn perustuvat metaheuristiset optimointialgoritmit

Tässä Pro gradu -tutkielmassa käsitellään yleisesti optimointia, metaheuristiikkoja ja parviälyä. Tutkielmassa esitellään muutamia luonnon inspiroimia parviälyalgoritmeja sekä vertaillaan niitä keskenään teoreettisesti ja numeerisesti. Tutkielmassa esitellyt vertailut on toteutettu kirjallisuuskatsauksena. Luonnon inspiroimat parviälyalgoritmit ovat metaheuristiikkoja, jotka perustuvat luonnossa elävien eläinlajien parvikäyttäytymiseen. Parvikäyttäytyminen juontaa juurensa parvessa elävien yksilöiden välisestä parviälystä, joka perustuu parven yksilöiden yhteiseen tavoitteeseen. Parviälyn periaatteena on, että parven yksilöiden välisen käyttäytymisen ja tiedonsaannin avulla syntyy toimiva kokonaisuus. Tutkielmassa esitellyt parviälyalgoritmit ovat muurahaisyhdyskuntaoptimointi, partikkeliparvioptimointi, mehiläisyhdyskuntaoptimointi, lepakkoalgoritmi, käkihaku ja tulikärpäsalgoritmi. Kyseiset parviälyalgoritmit ovat monikäyttöisiä erilaisten optimointitehtävien ratkaisemiseen, muun muassa niiden populaatiopohjaisuuden ansiosta. Lisäksi algoritmien numeerinen vertailu osoittaa muutaman algoritmin tehokkaan tavan saavuttaa jopa globaali optimi

EVALUATION OF A RUNNER’S PHYSIOLOGICAL PARAMETERS USING DIFFERENT SPRINT MODELS

INTRODUCTION: Hill’s model of sprinting, based on Newton’s second law of motion, uses two physiological parameters to characterize the sprinter, the maximum propulsive force per unit mass and the resistance-to-motion parameter related to the runner’s internal energy losses. Furusawa et al. (1927) suggested a resistive force law linear in the running speed. Later Keller (1973) and many others based their studies on Hill’s model. Senator (1982) added the effects of air resistance by a term quadratic in speed. Vaughan (1983) used a modification of these approaches by introducing a 0.7-power law. Recently, utilizing the rotational equation of motion for the leg and experimental data for stride frequency, we have shown that the internal and external resistive forces may well be approximated by a combination of linear and quadratic terms in running speed. We have also derived an expression for the internal resistive force in terms of physiological quantities. METHODS: The different models may be classified according to the resistive force law as linear (L), Vaughan (Va), quadratic (Q) and linearquadratic (LQ) models. We give analytical solutions for the distance-time relationships, except for the Va-model. We have used a numerical gradient method to fit the models with measured 100m data at ten equally spaced time stations of the 1988 Olympic Games in Seoul. Wind velocity and reaction times are also taken into account. RESULTS: By considering the residual errors we found that the best fit was given by the Va-model, followed by the LQ-, L-, and Q-models. The average residual error per time station for the Va- and LQ-models was about 0.01 s, which means a good fit throughout the run. We compared the values of the calculated physiological parameters with those in the existing literature. For the L-model the propulsive and resistive forces found by Vaughan and Matravers (1977) are in close agreement with ours, whereas those found by Woodside (1991) and Keller (1973) are too high, as can also be inferred from recent starting block data. For the parameters of the Va-model Vaughan (1983) obtained values somewhat lower than ours, using Ben Johnson, Carl Lewis and Linford Christie. This is to be expected, however, since Vaughan obtained his data for national university sprinters. As far as we know, the LQ-model has not been previously used. CONCLUSIONS: Our results show that the Va- and LQ-models best fit the Olympic 100 m data. There is a noteworthy difference between the interpretation of the linear resistive term in Hill’s theory and in the LQmodel presented in this paper: Hill and his colleagues invoked the concept of the viscosity of the muscles, while we arrived at the linear term by writing the rotational equation of the leg. It must be noted that already Fenn (1930) criticized the viscosity concept and attributed the resistive force to antagonistic muscles and other kinesiological factors. In view of our derivation of the LQ-model, the resistive force stems mainly from the rotational inertia of the leg, whereas the energy losses occur in the antagonistic muscles during the decelerating phases of the back and forth motion of the legs

Development of web tension in a winding nip

Today practically all winding devices apply a nip to the wound roll. In this winding method, radial pressure is applied by a winding drum to the wound roll at the point where the web enters the roll. This reduces the air entrainment into the roll and increases the tension of the web entering the roll. The wound roll internal stress profile is determined by this Wound-On-Tension (WOT). If the WOT along with the elastic moduli of the web are known, the internal stresses of the wound roll can be calculated. A winding simulation model predicting the internal stresses of a wound roll would provide a valuable tool for the optimal selection of the winding control parameters. When the incoming web enters the nip area its state of stress and strain changes significantly. An evaluation of these changes without any presumptions necessarily calls for a rigorous contact mechanical solution. The aim of the present paper is to calculate the surface tractions and the WOT due to the winding nip and, hence, provide means to predict the wound roll stresses as a function of the winding parameters.The contact mechanical model is based on the plane strain elastic solutions of the wound roll, winding drum and the wrapping and intervening web, combined with the indentation, stick and slip equations. A homogeneous elastic orthotropic material law for the roll, drum and web is used. The incoming web may slip with respect to the roll and drum, whereas slippage of the layers in the roll is not allowed (solid roll model). The stick-slip pattern within the contact zone is iterated using a variant of the Panagiotopoulos Process. Numerical calculations revealed a typical mechanism for the development of the nip-induced tension when the winding drum is hard and the coefficient of friction between the drum and web is larger than that between the web and roll. Due to the appearance of a double-sided slip zone in the vicinity of the trailing edge of the nip, the web moves faster than the wound roll and winding drum and, hence, the web tension increases, It is also shown that for a winding drum covered with a thin rubber cover, most of the web tension increase occurs at the winding drum wrap. In addition, the dependence of the nip-induced tension on the winding force, layer-to-layer friction, wound roll and winding drum radii, drum cover compliancy and the elastic constants of the web was studied numerically. The calculated results were in good qualitative agreement with the experimental ones

Strain-inducing mechanism of a rolling nip on a paper stack

The rolling of a cylindrical drum on a stack of separate paper sheets is studied using the finite element method. A two dimensional model under plane strain conditions is considered. The material of the sheets is modeled by a linearly elastic orthotropic constitutive law. The friction between the various contacting surfaces is modeled by the conventional Coulomb's law. As a result of the FEM-calculations the time development of the displacements, stresses and strains of the paper layers is obtained. The slip behavior at the various contacting surfaces is presented. The results indicate the existence of an instant center in the stack demonstrated earlier experimentally. The micro-slip pattern of the contacting surfaces in the nip area and, particularly, at the trailing edge of the nip, seems to be the main reason for the tightening effect of the nip. The results are compared to the corresponding results for a solid elastic block under the rolling cylinder

Contact mechanical approach to the winding nip

A contact mechanical model for the winding nip, consisting of the wound roll, winding drum and the intervening sheet, is presented. The roll and drum are modeled as linear, orthotropic, homogeneous cylinders with a rigid core. The elastic solutions for the cylinders are derived analytically in a series form. The sheet is modeled as a linear and orthotropic material as well. An approximate elastic solution for the sheet is obtained by assuming an internal stress distribution compatible with the boundary conditions (thin sheet approximation). The governing contact mechanical equations are presented and the appropriate form of the wound-on-condition of the sheet is presented

Two-drum winder run simulation model

A dynamic, analytical model for winder run simulations is presented. The model consists of elastic drums, deformable paper rolls and a rigid rider roll beam. A paper roll nip flexibility model is derived and a profound influence of paper roll properties on winder dynamics is demonstrated. The origin of winder vibrations due to specific vibrating paper grades is explained in detail. Winder drum design aspects against vibrations are studied. Finally, some practical measures to reduce winder vibrations are presented

Wound roll generated unstable vibration on a two-drum winder

Nip contact between the paper roll, winding drum and rider roll or some other nip roller may cause that the wound roll is deformed into a convex polygon. This deformation process is accompanied with a strong vibration. The conditions under which this phenomenon occurs depend very much on the web properties. For example, in the paper industry some bulky grades with a high layer-to-layer coefficient of friction are known to be prone to this unstable vibration.In this paper a simple wind-up model of a two-drum winder, capable of capturing quite comprehensively this phenomenon, is developed. The pattern formation is modelled via viscoelastic surface deformation. This results in a system of linear delay differential equations. Performing Laplace transformation to the system equations enables to study the stability of the system as a function of the web properties, nip drum stiffness, wind-up geometry and damping. The model parameters related to the viscoelastic surface deformation are measured experimentally for several paper grades.The paper is concluded by studying the system stability in a certain resonance condition. It is demonstrated that the system can be stabilised by changing the structural parameters of the winder